St. Paul is, like the twelve, an apostle of Christ (Alleluia), "he shall sit in one of the twelve seats and shall judge the world when the Son of Man shall Himself be seated on the throne which belongs to Him as Son of God" (Gradual and Gospel).
Following the example of St. Paul, let us show by our faith and by a new life that Jesus is God and that He is our King.
Scio cui credidi et certus sum, quia potens est depositum meum servare in illum diem, justus judex. Domine, probasti me, et cognovisti me: tu cognovisti sessionem meam, et resurrectionem meam.
I know whom I have believed, and I am certain that He is able to keep that which I have committed to Him against that day, being a just Judge. * Lord, Thou hast proved me and known me: Thou hast known my sitting down, and my rising up.
(2 Timothy 1:12 and Psalm 138:1-2 from the Introit of Mass)
Deus, qui univérsum mundum beáti Pauli Apóstoli praedicatióne docuísti: da nobis, quaesumus; ut, qui ejus hódie Conversiónem cólimus, per ejus ad te exémpla gradiámur.
O God, who hast taught the whole world by the preaching of blessed Paul the apostle, grant that we, who this day celebrate his conversion, may by following his example, be drawn unto Thee.
A reading from the Acts of the Apostles
And Saul, as yet breathing out threatenings and slaughter against the disciples of the Lord, went to the high priest, And asked of him letters to Damascus, to the synagogues: that if he found any men and women of this way, he might bring them bound to Jerusalem. And as he went on his journey, it came to pass that he drew nigh to Damascus; and suddenly a light from heaven shined round about him. And falling on the ground, he heard a voice saying to him: Saul, Saul, why persecutest thou me? Who said: Who art thou, Lord? And he: I am Jesus whom thou persecutest. It is hard for thee to kick against the goad. And he trembling and astonished, said: Lord, what wilt thou have me to do? And the Lord said to him: Arise, and go into the city, and there it shall be told thee what thou must do. Now the men who went in company with him, stood amazed, hearing indeed a voice, but seeing no man. And Saul arose from the ground; and when his eyes were opened, he saw nothing. But they leading him by the hands, brought him to Damascus. And he was there three days, without sight, and he did neither eat nor drink. Now there was a certain disciple at Damascus, named Ananias. And the Lord said to him in a vision: Ananias. And he said: Behold I am here, Lord. And the Lord said to him: Arise, and go into the street that is called Stait, and seek in the house of Judas, one named Saul of Tarsus. For behold he prayeth. (And he saw a man named Ananias coming in, and putting his hands upon him, that he might receive his sight.) But Ananias answered: Lord, I have heard by many of this man, how much evil he hath done to thy saints in Jerusalem. And here he hath authority from the chief priests to bind all that invoke thy name. And the Lord said to him: Go thy way; for this man is to me a vessel of election, to carry my name before the Gentiles, and kings, and the children of Israel. For I will shew him how great things he must suffer for my name's sake. And Ananias went his way, and entered into the house. And laying his hands upon him, he said: Brother Saul, the Lord Jesus hath sent me, he that appeared to thee in the way as thou camest; that thou mayest receive thy sight, and be filled with the Holy Ghost. And immediately there fell from his eyes as it were scales, and he received his sight; and rising up, he was baptized. And when he had taken meat, he was strengthened. And he was with the disciples that were at Damascus, for some days. And immediately he preached Jesus in the synagogues, that he is the Son of God. And all that heard him, were astonished, and said: Is not this he who persecuted in Jerusalem those that called upon this name: and came hither for that intent, that he might carry them bound to the chief priests? But Saul increased much more in strength, and confounded the Jews who dwelt at Damascus, affirming that this is the Christ.
From the Catholic Encyclopaedia: http://www.newadvent.org/cathen/11567b.htm